Method of making bearing materials

ABSTRACT

A method of making composite material which provides low friction surfaces for materials in rolling or sliding contact. The composite material is self-lubricating and oxidation resistant up to and in excess of about 930° C. The composite material is comprised of a metal component which lends strength and elasticity to the structure, a fluoride salt component which provides oxidation protection to the metal but may also enhance the lubrication qualities of the composite.

ORIGIN OF THE INVENTION

The invention described herein was made by an employee of the U.S.Government and may be manufactured and used by or for the Government forgovernmental purposes without the payment of any royalties thereon ortherefor.

RELATED APPLICATIONS

This application is a division of application Ser. No. 764,245, filedJan. 31, 1977, which is a division of application Ser. No. 616,528,filed Sept. 25, 1975, and now abandoned which is a division ofapplication Ser. No. 513,611, filed Oct. 10, 1974, and now U.S. Pat. No.3,953,343.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to making composite bearing materialswhich are self-lubricating and oxidation resistant over a broadtemperature range up to and preferably in excess of about 930° C.Composites of this invention are comprised of distinct metallic, glassand fluoride components.

These novel composites may be fabricated by infiltration of a porous,sintered metal with molten glass and fluorides as is well-known in thefield of powder metallurgy. Optionally, the constituents of thecomposite may be co-deposited by plasma-spray techniques on a suitablesubstrate.

2. Description of the Prior Art

Lubrication of mating surfaces in frictional engagement has long posedproblems of wear (e.g., abrasive, adhesive, chemical and fatigue) andoverheating of machine parts which subsequently fail prematurely as themanifest result thereof. Typically, oils and greases have been employedto mitigate the deleterious effects of heat and abrasion by virtue oftheir very low coefficients of friction and relatively long-lifeproperties. However, as technology progressed and thus imposed moresevere operating conditions, most notably, higher operatingtemperatures, it was found that the lubrication properties of fluidswere inherently limited, thus ultimately limiting the scope of theadvanced design.

In response to the inherent deficiencies of fluid lubricants, solidlubricants emerged as clearly superior in extreme environmentalconditions such as high temperatures at which fluids decompose or, onthe other hand, extremely low temperatures at which fluids freeze.Additionally, it has been shown that many solid lubricants are extremelyeffective in chemically active environments which readily decomposefluid lubricants via chemical attack.

Moreover, solid lubricants effect overall savings in many systemsinsofar as vast weight reduction can be achieved through elimination ofpumps, heat exchangers, recirculation systems, and the like, as well asthe elimination of seals ofttimes necessary to isolate lubricating andworking fluids. Similarly, replenishment of contaminated fluids isvitiated by the use of solid lubricants.

Perhaps the first and most widely employed solid lubricant was graphite.Graphite is formed as a covalently bonded carbon solid of hexagonalstructure which may be viewed microscopically as two-dimensional planarmolecules occupying basal plane positions, stacked one on top of anotherand held together by weak, secondary van der Waals forces. The facilitywith which these "sheets" may readily part along basal planes providesthe well-known lubrication qualities of graphite.

However, graphite possesses severe deficiencies as a lubricant inextreme conditions. It has well been demonstrated that the lubricatingqualities of graphite are predicated upon its ability to absorb gas,moisture of hydrocarbon vapors before the property of low shear strengthis attained. While the gases and water vapor present in a normalatmosphere are usually sufficient to ensure an adequate supply ofadsorable material, at high altitudes or under vacuum conditions, forexample, desorption occurs with the subsequent loss of lubricationfeatures. Additionally, at temperatures over approximately 95° C.,adsorption is significantly decreased with a concomitant decrease inlubrication properties.

To minimize these deficiencies, it has been shown that graphite may bereacted with fluorine gas to yield an improved solid lubricant of theform CF_(x) where x may vary from approximately 0.3 to 1.1. While thisintercalation compound of graphite is capable of providing lubricationwithout the need of an adsorbed vapor or impurity up to temperatures ofapproximately 500° C., the chemical reaction must be carefullycontrolled to yield suitable properties. Then too, oxidation ordissociation at temperatures approaching 500° C. remain persistentproblems in graphite systems regardless of the fabrication techniques orchemical alteration thereof.

Similar to graphite are such solid lubricants as molybdenum disulfideand tungsten disulfide which are also hexagonal-layered and whose shearproperties are anisotropic, with preferred easy shear parallel to thebasal planes of the crystallites. In contradistinction to graphite,neither of this disulfides requires the presence of an adsorbed layer toachieve lubrication properties; however, these disulfides too aretemperature limited, albeit at higher temperatures approaching 400° C.where decomposition by oxidation occurs.

Moreover, in highly oxidizing conditions it is well known that thepresence of molybdenum greatly contributes to the catastrophic oxidationof many engineering alloys. This catastropic or accelerated oxidationresults as molybdenum oxidizes to MoO₃ at temperatures greater than 400°C. This oxide of molybdenum will melt at approximately 795° C., and ithas been suggested that this low-melting oxide phase may then act as anflux to dislodge or dissolve protective films. Additionally, eutecticcombinations of the molybdenum oxide and other oxides present willfurther reduce the melting point, thus aggravating the structuraldegradation attendant this high temperature oxidation.

While the effectiveness of the above-noted layer-lattice lubricants maybe greatly enhanced through resin bonding techniques, severe limitationsare yet presented as temperaturs increase within the range of interest.Still too the problem of catastrophic oxidation are not overcome by suchresin bonding of the lubricant.

The breakthrough in high temperature lubrication came with the discoverythat various fluorides provide low friction surfaces under extremes oftemperature and ambient chemical environment. Note, for example, U.S.Pat. Nos. 3,157,529, 3,419,363 and 3,508,955 each to H. E. Sliney andassigned to the National Aeronautics and Space Administration. Each ofthese patents relates generally to solid lubricants comprised of,interalia, fluorides.

More particularly, U.S. Pat. No. 3,157,529 discloses fluoride lubricantcoatings applied as a film to the surface to be lubricated, whichcoatings are basically comprised of calcium fluoride and a suitableceramic binder therefor. While such techniques have proved extremelyeffective in the field of high-temperature solid-lubricant coatings, theuseful life of such coatings is limited. When the coating eventually isworn away, the lubricant cannot be readily replenished and lubricationceases. A method whereby solid lubricant is replenished as wear takesplace is clearly desirable. Self-lubricating composites are an approachto accomplish this replenishment.

To reduce the problems of film-type solid lubricants, composite bearingmaterials containing fluoride lubricants were subsequently developed bySliney. For example, U.S. Pat. No. 3,419,363 discloses such a compositecomprised of a porous metal impregnated with Group I or Group IImetallic fluorides with the eutectic composition of barium fluoride andcalcium fluoride as the preferred lubricant. However, such compositeshave posed new problems insofar as the porous metal component providesgreatly increased surface area as opposed to that of solid substrates.Accordingly, high temperature oxidation of these porous, sintered metalsposes significant problems at temperatures exceeding 700° C.

Accordingly, a need exists for improved high-temperature,self-lubricating materials which exhibit the excellent lubricatingqualities of fluoride-containing composites and yet are not susceptibleto high temperature oxidation. The need for such materials is presentlybecoming critical in advanced aircraft where aerodynamic heating atspeeds of Mach 3 and higher can result in vehicle skin temperatures wellabove the temperature limitations of presently available air framebearings. As an extreme case, it is predicted that the maximum skintemperature for the Space Shuttle Orbitor during re-entry will approachor exceed 1100° C. Air frame bearings and control surface seals for theorbitor proximate these heated surfaces must be capable of hightemperature operation without degradation. Other areas in which hightemperature lubrication has become increasingly more important includesliding contact seals for automotive turbine regenerators, shaft sealsfor turbo pumps, piston rings for high performance reciprocatingcompressors, hot glass processing machinery, and the like.

SUMMARY OF THE INVENTION

To obviate the deficiencies in the prior art, it is the primary objectof this invention to provide an improved method of makingself-lubricating bearing materials which are oxidation-resistant up toand preferably in excess of about 930° C.

It is also an object of this invention to provide self-lubricating,oxidation-resistant bearing materials comprised of a heat-resistantmetal component, an oxidation-inhibiting glass component and alubricating fluoride component.

It is yet another object of the invention to provide theseself-lubricating, oxidation-resistant bearing materials fabricated byplasma-spray co-deposition of the metal, glass and fluoride components.

It is still a further object of this invention to provide a method offabricating self-lubricating, oxidation-resistant bearing materialswhich are durable and yield plastically under unit loads of at leastMN/m² at temperatures up to and in excess of about 930° C.

It is another object of this invention to fabricate self-lubricating,oxidation-resistant bearing materials simply, yet efficiently, and atlow cost.

Further objects of this invention will become apparent to those skilledin the art from examination of the following detailed description of theinvention.

It has now been determined in accordance with this invention that lowfriction surfaces exhibiting self-lubrication and oxidation resistanceup to and in excess of about 930° C. may be formed as a composite of ametallic constituent which lends strength and elasticity to thestructure, a glass component which provides oxidation protection to themetal and may also contribute to reduced wear and finally, a fluoridecomponent which provides lubrication. The composite of this inventionmay be fabricated as a porous, sintered metallic matrix which isinfiltrated with molten glass and fluoride or, optionally, a suitablesubstrate with metal, glass, and fluoride components co-depositedthereon by plasma-spray techniques. The lubricating material of thepresent invention will effectively preclude galling from roomtemperature to and in excess of 930° C., but is particularly effectiveover the range 530°-930° C. at which temperature the glass andparticularly the fluorides are soft enough to form a smear or glaze oflubricating film on the surface. These novel composites are easilymachined and exhibit plastic response over the temperature range ofinterest.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The principle of operation of the self-lubricating, oxidation-resistantcomposite of the invention rests upon the ability of the metalliccontent of the composite to provide strength and elasticity to thestructure; the glass will provide oxidation-protection to the metal andmay additionally enhance the lubrication quality of the fluoridecomponent. During the sliding process, any wear that takes place exposesmore fluoride lubricant thereby preventing an increase in wear rate orgalling of the surfaces. The lubricating material will effectivelyprevent galling from room temperature to at least 930° C., but it isparticularly effective from 530° to 930° C. at which temperature theglass and particularly the fluorides are soft enough to form a smear orglaze of lubricating film on the surface.

As noted above, the function of the metallic component is to providestructural strength to the instant composites over the temperature rangeof interest and under bearing loads which oftentimes exceed unitstresses of approximately 35 MN/m². Accordingly, this metal componentmay be selected from any of the well known high temperature alloys, andmost notably alloys of iron, cobalt or nickel. Specific examples of suchhigh temperature alloys which may be used to fabricate the composites ofthe instant invention are: for iron -- austenitic and ferritic stainlesssteels, for example; for cobalt -- super-alloys containing significantchromium such as H.S.6B, H.S. 21, and H.S.25, and for nickel --super-alloys such as the inconels, nichromes, Rene 41, and the like.Numerous other high temperature alloys are equally well suited toprovide the necessary structural strength at the temperatures ofinterest and are familiar to those skilled in the art. However, it hasbeen determined that the metal component of the composite is preferablya high nickel or cobalt alloy, i.e., one containing greater than 50%nickel or cobalt, with significant chromium content, i.e., greater than10%. Most preferred is an 80% nickel, 20% chromium alloy.

Optionally, the metallic component of the composite may contain silver,gold or alloys thereof, it being understood that the optional silveradditions limit the maximum serviceable temperature to about 820° C. asthe result of a melting point of about 850° C. for this component. Suchadditions will improve the low temperature lubricating characteristicsof the composite thereby expanding their effective operating range.While these silver and/or gold additions may be present from 0 to 50% byweight, it will be appreciated that the time-temperature profile for thecomposite bearing material will necessarily predicate the amounts ofthese components, particularly the relatively low melting silver.Accordingly, bearings which are put into prolonged, high-temperatureservice, i.e., more than approximately 90% of their operating time attemperatures in excess of approximately 500° C. need incorporate onlyminor percentages of precious metal components such as 0 to 10%.Contrariwise, bearings expected to be subjected to short-lived, rapidfluctuations up to high temperatures of approximately 900° C. buttypically operated within an ambient temperature range of about roomtemperature to 500° C. may incorporate significant percentages of thesesilver and/or gold additions, i.e., 10 to 50%. Accordingly, it canreadily be seen that the instant composites may be tailored to meetnumerous design criteria.

Turning now to the fluoride component of the self-lubricatingcomposites, it will be appreciated that numerous fluoride salts may beemployed to achieve the desired lubrication features. Illustrative ofsuch fluoride salts are those of Group I and Group II metals of thePeriodic Table of Elements as well as fluorides of rare earth(lanthanide series) metals of the Periodic Table of Elements. Preferredfor providing the lubricating qualities of the composites of thisinvention are eutectic mixtures of the foregoing fluorides. Alsopreferred are the fluorides of calcium and barium, while most preferredis the eutectic composition of calcium fluoride and barium fluoride.

With regard to the glass component of the topic composites, it has beendetermined to be highly beneficial to employ a silicate glass [i.e., aglass containing from 55% to 80% silica] which is high in concentration,[i.e., at least about 20% by weight] of oxides of divalent ions of GroupII metals, especially Ba⁺⁺, and low [i.e., less than about 10% byweight] in oxides of monovalent ions of Group I metals such as an Na⁺.That is, it is most beneficial to employ Group II silicate networkmodifiers in preference to the more conventionally employed Group Imodifiers found typically in commercial glasses such as the commonsoda-glasses. Such a constraint may be explained, at least in part, bythe observation that glasses low in Na⁺ content have an atomicarrangement which is less favorable for diffusion of transition metalions such as Fe⁺⁺, Co⁺⁺, Ni⁺⁺, and Cr⁺⁺⁺. Accordingly, these low sodiumion glasses will provide better protection of the metallic constituentsof the composite against oxidation reactions such as these which arediffusion-rate controlled.

A preferred glass composition within the scope of the instant inventionis comprised of 10 to 50% BaO; 0 to 30% Na₂ O and/or K₂ O; 0 to 15% CaO,and, balance SiO₂. While it has been determined that glasses fallingwithin the foregoing preferred compositional limits will effectivelyinhibit oxidation of the metallic component of the composite, the mostpreferred glass composition is one comprised of 20% BaO, 10% K₂ O, 10%CaO, 60% SiO₂.

Having thus described the individual components of the topicself-lubricating, oxidation-resistant composites of the presentinvention, it will be appreciated that each of the metal, fluoride, andglass components may be present in varying amounts. For example, in viewof the fact that the metallic component of the composite isfundamentally present to provide structural integrity, bearing surfacessubjected to fairly low loads, i.e., 7 MN/m² or less, may functionadequately with a metallic content of from 20 to 40% relative to theweight of the entire composite. Contrariwise, bearing surfaces subjectedto high unit loads, i.e., loads above 35 MN/m² may require as much as80% metallic constituent to provide the necessary structural strength.Accordingly, the skilled artisan may incorporate the metallic componentin amounts ranging from 20 to 80% depending upon the design criteria ofthe desired application. Similarly, depending upon the degree ofoxidation-inhibition desired when viewed against the oxidizing nature ofboth the ambient environment and metal component selected, the combinedglass and fluoride salt content may be present within the range of 20 to80%.

With regard to this combined fluoride salt glass content, thefluoride-to-glass ratio may extend from 1:2 to 2:1. Should the ambientsurroundings of the composite bearing material by highly oxidizing,there may be provided up to two-thirds oxide-inhibiting glass relativeto the fluoride salt content while less oxidizing atmospheres may allowfor as low as one-third glass content relative to the fluoride componentof the composite. However, under most circumstances, the most preferredratio between fluoride salt content and glass content is 1:1.

Accordingly, in view of the foregoing, self-lubricating,oxidation-resistant bearing composites may be comprised of from 20 to80% high-temperature resistant metallic component; 0 to 50% silver, goldor alloys thereof; and, 20 to 80% combined lubricating fluorides andoxide-inhibiting glass. A preferred composition comprises 60 to 70% of ametallic constituent selected from the group of high temperature iron,cobalt, and nickel alloys; 15 to 20% of a lubricating fluoride saltselected from the group of calcium fluoride, barium fluoride andmixtures thereof; and, 15 to 20% of a glass comprised of from 10 to 50barium oxide, 0 to 30% sodium oxide and/or potassium oxide, 0 to 15%calcium oxide and balance silica.

A most preferred composite according to the present invention iscomprised of 67% of an 80 nickel, 20 chrome alloy, 161/2% of bariumfluoride-calcium fluoride eutectic, and 161/2% of a glass comprised of20% BaO, 10% K₂ O, 10% CaO, and 60% SiO₂. In the case of plasma-sprayedcomposites, the fluoride eutectic may be replaced with the singlefluoride, CaF₂.

Having thus described the materials which may be employed to fabricatethe composites of the present invention as well as clearly setting forththe most preferred composition, the present invention will be describedwith reference to the following fabrication technique for the subjectbearing material.

Plasma Spray Codeposition

The preferred fabrication technique of the present invention invisionsthe formation of the self-lubricating composite from plasma sprayedmetal-glass-fluoride powders. Numerous important advantages are attainedfrom employing plasma-arc spray techniques as opposed to theaforementioned infiltration of porous sintered bodies. Most notably, theplasma-spray codeposition of the various constituents of this compositedirectly upon the supporting substrate precludes the necessity of theadditional process step of brazing or otherwise attaching thelubricating composite to the desired surface. With respect to thisadditional step of brazing, etc. which typically requires heating thesubstrate into a temperature range possibly harmful to the metallurgicalproperties thereof, the plasma-spray technique need not heat thesubstrate over approximately 150° C. thus preserving the effects of anyprior heat treatment, reducing the possibility of alloy segregation,etc. Additionally, the plasma-spray technique is simpler, moreeconomical and faster than impregnation of porous, sintered metalworkpieces.

In carrying out the plasma-spray method, glass frit is prepared in anymanner well known to those skilled in the art: e.g., ball milling asuitable glass composition. The glass frit is sized to particles of 125microns and is thence mixed with the desired metal powder and fluoridelubricant powder.

The underlying substrate surface upon which the bearing composite is tobe codeposited should be grit blasted or otherwise cleaned to removesurface films, foreign materials and the like. The composites may thenbe sprayed to a thickness from 0.010 centimeters to 0.060 centimetersand subsequently machined back to a working thickness of fromapproximately 0.005 centimeters to approximately 0.050 centimeters.

Techniques employed for such plasma-arc codeposition are well known inthe prior art. Note, for example, U.S. Pat. Nos. 3,540,942 and3,640,755, each of which deals with conceptually similar techniques forthe plasma-arc spraying of metallic materials. More particularly, noteNASA Technical Memorandum TMX-71432, "Plasma-Sprayed Metal-Glass andMetal-Glass Fluoride Coatings for Lubrication to 900° C." by H. E.Sliney, incorporated herein by reference, and relied upon. It will beappreciated, however, that other metal-spray techniques may likewise beemployed to achieve the codeposition of the metal-glass-fluorideconstituents of the topic composites. Such other techniques, as areobvious to those skilled in the art, include, for example, flame-sprayand electric-arc spray such as set forth in Manufacturing Processes andMaterials for Engineers, Doyle et al., 2nd Edition, Prentice Hall, NewJersey, 1961, pages 376-378.

Regardless of the fabrication technique selected from those mentionedabove, the composite bearing materials of this invention may be surfaceenriched in the lubricant by a thin fluoride spray film as previouslydescribed or by subsequent heat treatment in air at from 760° C. to 900°C. for 4 to 24 hours. Such a heat treatment will cause slight exudationand solid state migration of fluorides along the surface and furtherserves the beneficial purpose of mildly pre-oxidizing the exposed metal.Additionally, the surfaces will become entirely covered with a combinedfluoride-oxide film which is highly desirable to prevent directmetal-to-metal adhesive contact during sliding.

Additionally, it should be noted that the self-lubricating,oxidation-resistant composites of this invention are easily machinableand may be put into service as machined, as honed, or finished withabrasive paper. Under bearing loads of 35 MN/m² or greater and attemperatures up to at least 930° C. these composites will yieldplasticly thus precluding failures due to brittle fracture and reducingfatique tendencies attendent high-cycle operation typical of bearingapplications.

To further illustrate the objects and advantages of the presentinvention, the following specific examples will be given, it beingunderstood that same are intended to be merely illustrative and in nowise limitative.

EXAMPLE 1

60 grams of Haynes Stellite 6B powder and 10 grams of silver, each of-125 mesh, are combined with 15 grams of glass frit of 125 micronsprepared by ball milling 20% barium oxide, 10% potassium oxide, 10%calcium oxide and 60% silicon oxide; and, 15 grams of calcium fluoride-- barium fluoride eutectic powder. This mixture is plasma-arc sprayedon an AISI 440c stainless substrate which is prepared by grit blastingto remove any foreign matter. The metal, glass and fluoride composite isco-deposited to a thickness of 0.050 centimeters and allowed to cool.The composite is then honed to a thickness of 0.025 centimeters and isready for service.

EXAMPLES 2-7

Examples 2-7 are prepared in the same manner as that given for Example 1and are composed of those materials outlined in Table 2, which materialsare selected from those set forth in Table 1.

                  TABLE 1                                                         ______________________________________                                                A        B        C      D      E                                                                      Hastelloy                                                                            80% Ni:                               Metal:  AISI 310 AISI 330 H.S. 6B                                                                              G      20% Cr                                ______________________________________                                        Glass:                                                                        BaO     10       15       20     25     30                                    Na.sub.2 O                                                                            --       --       --     --      5                                    K.sub.2 O                                                                             --       --       10      5      5                                    CaO     10       10       10      5      0                                    SiO.sub.2                                                                             80       75       60     65     60                                    Fluorides:                                                                    CaF.sub.2                                                                             100      --        50*   50     50                                    BaF.sub.2                                                                             --       100      50     --     --                                    MgF.sub.2                                                                             --       --       --     --     --                                    LiF     --       --       --     --     50                                    SrF.sub.2                                                                             --       --       --     50     --                                    ______________________________________                                         *eutectic                                                                

                  TABLE 2                                                         ______________________________________                                        Example  Metal           Glass     Fluoride                                   ______________________________________                                        1        60% C + 10% Ag  15% C     15% C                                      2        30% E + 30% Ag  15% C     25% A                                      3        30% C + 30% Ag  15% C     25% A                                      4        67% E           161/2% C  161/2% A                                   5        70% A           20% D     10% C                                      6        40% D           20% B     40% B                                      7        80% E           20% E     0                                          ______________________________________                                    

While the invention has been described and illustrated with reference tocertain preferred embodiments thereof, those skilled in the art willappreciate that various modifications, changes, omissions andsubstitutions may be made without departing from the spirit of theinvention. It is intended, therefore, that the invention be limited onlyby the scope of the following claims.

What is claimed is:
 1. A method for fabricating a self-lubricating,oxidation-resistant article comprising the steps offorming a frit of aglass capable of inhibiting oxidation in a metal capable of providingstrength and elasticity to a temperature up to and in excess of about930° C., mixing said glass frit with powders of said metal and powdersof a fluoride salt capable of providing lubrication thereby forming acomposition of matter, co-depositing the mixture of said metal, saidfluoride salt and said glass on a substrate by means of plasma-arcspraying to form a coating having a thickness from about 0.010centimeter to about 0.060 centimeter, and machining said coating to athickness between about 0.005 centimeter and about 0.050 centimeter. 2.A method for fabricating a self-lubricating, oxidation-resistant articleas claimed in claim 1, further comprising heat treating saiddeposit-containing substrate at a temperature of from about 760° C. to900° C. for a period of from about 4 to 24 hours.
 3. A method forfabricating a self-lubricating, oxidation-resistant article as claimedin claim 1, wherein said article comprises:(a) 20%-80% of an alloyconsisting essentially of 80% Ni and 20% Cr; (b) 10% to 40% of CaF₂ ;(c) 10% to 40% of a glass consisting essentially of 20% BaO, 10% K₂ O,10% CaO and 60% SiO₂ ; and (d) 0-50% Ag, Au or alloys thereof.
 4. Amethod for fabricating a self-lubricating, oxidation-resistant articleas claimed in claim 1, wherein said article comprises:(a) 67% of analloy consisting essentially of 80% Ni and 20% Cr; (b) 161/2% of CaF₂ ;and (c) 161/2% of a glass consisting essentially of 20% BaO, 10% K₂ O,10% CaO and 60% SiO₂.
 5. A method for fabricating a self-lubricating,oxidation-resistant article as claimed in claim 1 wherein the glass fritis formed by ball milling.
 6. A method for fabricating aself-lubricating, oxidation-resistant article as claimed in claim 1wherein the glass frit is sized to particles of 125 microns.
 7. A methodfor fabricating a self-lubricating, oxidation-resistant article asclaimed in claim 1 including the step ofgrit blasting the surface ofsaid substrate prior to co-depositing the glass, metal and lubricant.